In a news release, Tracy called it an honor to serve the constituents in his district.

“I’m proud of my record over the past 13 years and I’m thankful for the many friendships I’ve made along the way,” said Tracy, who thanked former Lt. Gov. Ron Ramsey and Lt. Gov. Randy McNally.

"This is a great opportunity to serve my nation and my state doing something I am truly passionate about. I look forward to working with Secretary (Sonny) Perdue to make a difference in rural Tennessee."

Tracy's departure from the legislature was expedited because the appointment does not require congressional approval.

With the resignation coming Monday, a special election will be required. State law requires a special election to take place if there is a vacancy in a Senate seat more than a year before the next general election.

The general election takes place Nov. 6, 2018.

Tracy's resignation was required by the state Constitution, thus he could not wait until Wednesday to resign, which would have not have triggered a special election. Vacancies within one year of the general eleciton are filled through an appointment.

Two other state senators — Mark Norris and Doug Overbey — are awaiting congressional approval after Trump nominated them to become a federal judge and U.S. Attorney, respectively.

Gov. Bill Haslam has yet to order the special election, which by law must be held within 60 days of him issuing what is called a writ of election.

Given the timing of a special election could come in the midst of the 2018 legislative session, local officials could opt to appoint a placeholder to serve until the election.

Beyond the special election for Tracy's seat, another will be held Tuesday after the resignation of Mae Beavers, who exited the Senate amidst her run for governor. Tuesday's election is a primary, with only Rep. Mark Pody, a Republican, and Democrat Mary Alice Carfi on the ballot. They will square off in a general election set for Dec. 19.

When Beavers resigned, Tracy questioned the timing, saying it would have been "more conservative" to wait until November when a special election would not be required.

On Monday, Reeves, who is CEO of Murfreesboro-based TwelveStone Health Partners, and Carr said they are planning on entering the race.

Reeves thanked Tracy for his service, adding that a formal release announcing his candidacy would be sent out Tuesday.

Reeves is the lone officer of Reeves Family PAC, a political action committee whose treasurer is prominent GOP fundraiser Rachel Barrett. Earlier this year the PAC donated $5,000 to Randy Boyd and another $1,000 to U.S. Rep. Marsha Blackburn's campaign committee.

Carr, a tea party-aligned former lawmaker, unsuccessfully challenged U.S. Sen. Lamar Alexander in 2014 and U.S. Rep. Diane Black in 2016. Carr served in the state House from 2008 to 2014.

In his own news release, Carr said, "We are going to need men and women in the Tennessee state Senate with the proven experience to stand firm with Tennessee’s working families."

Reach Joel Ebert at jebert@tennessean.com or 615-772-1681 and on Twitter @joelebert29.